1. Field of the Invention
This invention relates to vascular prostheses of polytetrafluoroethylene.
2. Description of the Prior Art
Vascular prostheses made of knitted or woven fabric of a polyester (e.g. Dacron polyester, a trademark of E.I du Pont de Nemours and Co., Inc.) or of sheets of polytetrafluoroethylene are currently available, or have been described in the art. Expanded polytetrafluoroethylene (ePTFE) tubes have a microporous structure consisting of small nodes interconnected with many tiny fibrilla. EPTFE is extruded into tubes to make vascular grafts. Although vascular grafts constructed using such material are generally clinically successful, there is a tendency to leak blood at suture holes where the graft is attached to a patient. Because of the generally non-resilient characteristics of ePTFE material, suture needles create a larger hole in the sheet than the suture. There is a tendency for blood to leak around the sutures. Intraoperative measures taken to reduce or eliminate bleeding prolong operation times and are clearly undesirable. Such measures may include compression or other physical intervention.
Previous solutions to the problem of suture hole leakage have relied on filling the porous structure of the ePTFE material with a bioresorbable sealant. For example, Okita, U.S. Pat. No. 4,193,138, proposed introducing a water-soluble polymer into the pores of the ePTFE material and then treating the polymer to render it water-insoluble. Weadock et al., U.S. Pat. No. 5,665,114, proposed filling the pores with solid biocompatible material of natural origin. A water-soluble substance is introduced into the pores and treated to render it water-insoluble.
In connection with grafts made with knitted or woven fabrics, materials such as collagen or gelatin have been applied to the highly porous surface of such textiles. See, for example, U.S. Pat. Nos. 3,272,204; 4,747,848; 4,842,575 or 5,197,977. The materials can be expected to penetrate into the voids produced by the woven or knitted structure of the fabric and thus reduce blood leakage throughout the entire fabric, as well as at locations where sutures pass through the fabric. Of course, since fibers of the fabric will spread apart to allow passage of the suture needle and then return to a closer configuration adjacent a suture, the problem of suture hole leakage in fabric grafts is not as severe as in ePTFE grafts.
The prosthesis of our invention seeks to overcome the limitations of the prior art by providing an ePTFE vascular graft having a substantially uniform coating of bioresorbable gel on an outer surface. The method of application causes the coating to be confined substantially entirely to the outer surface, meaning that there is minimal penetration of the coating into the pores of the ePTFE material. Preferably, the bioresorbable gel is plasticised with glycerol.